An ink printing system

Abstract: An ink printing system including a device (8) for drying the ink jet images printed on the surface of a substrate (2) by the system including a plurality of nozzles (14) that direct a small volume of air onto the printed image at as high a velocity as possible without disturbing the wet image. The air so delivered while it must be dry, does not have to be heated to effectively dry the image. However, the drying time can, if desired, be reduced by increasing the air temperature. The use of high velocity air creates what is known as "skin effect" to dry the ink where the outer surface of the ink is quickly dried.

Description: The invention relates to an ink printing system and, more particularly, to an improved device for drying the ink jet images. Ink printing systems that utilise ink jet printers find application in a wide variety of printing applications. One such application is the printing of images, such as expiration dates and lot numbers, on cans, bottles and the like, on high speed automated production lines. Typically, the cans or bottles are filled with product, capped and labelled. The labelling process includes the application of the ink jet images directly to a surface of the cans and bottles and/or the labelling therefor. Because the ink jet imaging process occurs as part of the high speed operation of the production lines, it must be carried out rapidly and efficiently, i.e. the images must be applied and dried for further handling in a matter of seconds. The ink jet printers used in these high speed applications typically include an ink jet nozzle having an orifice providing a stream of ink. A piezoelectric device surrounds and acts upon the nozzle to cause the formation of drops as the ink leaves the nozzle orifice. The drops are selectively charged by a charging electrode and pass through a deflection field. The deflection field is created by opposed upper and lower electrodes where one electrode is connected to a power supply and the other electrode is grounded, or connected to a power supply of opposite polarity. The deflection field deflects selected drops to cause them to strike the substrate being marked, i.e. the can or bottle, to create a desired ink jet image. The drops that are not deflected to the substrate are caught by an ink catcher that returns the drops to the ink system for reuse. Typical ink jet printers are disclosed in U.S. Patent No. 4,845,512 issued to Arway and U.S. Patent No. 5,196,860 issued to Pickell et al. As will be apparent from the foregoing, the ink drops applied to the substrate, i.e. the can, bottle, or paper labelling, will be wet immediately after application. Because ink jet printers are used in high speed applications, the wet ink presents handling problems in that the wet ink can be easily smeared, or smudged. Thus, it is desired to dry the ink drops after the substrate, on which the ink jet image is formed, has left the printer. Known ink jet image driers typically consist of a heating element and blower positioned downstream of the printing station. The blower forces air over the heating element and onto the newly printed image. The blowers used in this process typically move the air at low pressure and high volume, i.e. of the order of 0.047 m 3 /sec to 0.094 m 3 /sec (100 to 200 cubic feet per minute), to transfer the heat to the printed image by convection and/or radiation. A disadvantage of this process is that it utilizes a large amount of air and electrical energy and is relatively inefficient and slow. As a result of this, the operating cost of the drier is relatively high. Furthermore, because a large volume of hot air is used, the metal components that form part of production line are exposed to the heated air and become extremely hot resulting in a safety hazard. Moreover, if the production line stops for any reason, the stationary product in front of the heater is heated, by the radiating heat, to a level that could damage the product, or in the case of paper, could start a fire. Finally, the blowers used in this process are large and noisy. EP-A-0364425 discloses a drying section equipped with blowing nozzles, each of which is intended to direct an air stream onto print material carrying wet print. During a print drying process, respective nozzles are located at a distance of less than 10 mm from the print, and the velocity of the air stream adjacent respective nozzles exceeds 100 m/sec, the time duration of the air streams being shorter than 10 sec, preferably between 1 and 5 sec for surface drying the wet print. It is an object of the present invention to provide an ink printing system for applying an inked image to a substrate having a safer, less expensive and more efficient device for drying the ink jet images on a substrate. The invention provides an ink printing system for applying an inked image to a substrate including a dewatering device for removing moisture from the substrate, a printhead for applying the inked image to the substrate, a drier for drying the inked image on the substrate and means for moving the substrate past the dewatering device, the printhead and the drier, characterised in that, the drier comprises an air chamber including a plurality of nozzles in communication therewith, for directing air at the inked image on the substrate, and means for delivering air under pressure to said chamber, in that the nozzles are adapted to deliver the air at the inked image at high velocity and low volume and in that the nozzles are angled (∝) such that the air has a velocity component in the direction of travel of the substrate, effecting an increase in the period of time during which the air contacts the area of the substrate to be dried. The angle (∝) of the nozzles can be in the range 0 and 25 degrees relative to a line perpendicular to the direction of travel of the substrate. The nozzles are at an angle (B) relative to the horizontal to control the direction in which the air moves after contacting the substrate and to thereby control the width of the heated area. The preferred value of angle (B) is approximately 25 degrees relative to the horizontal. The velocity of the air can be in the range 25.4 m/sec and 50.8 m/sec (5,000 and 10,000 feet per minute) and the volume of air moved can be in the range 0.00047 m 3 /sec and 0.0047 m 3 /sec (1 and 10 cubic feet per minute). The air directed at the inked image is heated to a temperature in the range 37.7 °C and 316° C (100 and 600 degrees Fahrenheit). The heating can be effected by a heating element located either in, or outside, the chamber. The system further includes means for regulating the pressure of the air delivered to the chamber thereby to control the speed of air from the nozzles. Thus, the ink jet image drier consists of a plurality of nozzles that direct a small volume of air onto the printed image at a high velocity. The air velocity is maintained as high as possible without disturbing the wet ink image. The specially designed nozzles of the invention allow the air to be delivered to the printed image area without warming the entire area. The air so delivered, while it must be dry, does not have to be heated to effectively dry the image. However, the drying time can, if desired, be reduced by increasing the air temperature. The use of high velocity air creates what is known as "skin effect", where the outer surface of the ink is quickly dried such that the ink image can be handled thereafter. The foregoing and other features according to the present invention will be better understood from the following description with reference to the accompanying drawings, in which: Figure 1 diagrammatically illustrates, in a front view, an ink printing system according to the present invention for use on a high speed production line; Figure 2 diagrammatically illustrates, in a top view, the drier illustrated in Figure 1 of the drawings; Figure 3 diagrammatically illustrates, in an end view, the ink printing system illustrated in Figures 1 and 2 of the drawings; Figure 4 diagrammatically illustrates, in a section view taken along a line 4-4, the drier forming part of the system illustrated in Figure 3 of the drawings; and Figure 5 diagrammatically illustrates, in a view taken along a line 5-5, the system illustrated in Figure 3 of the drawings. The ink jet printer section of a bottle filling production line is diagrammatically illustrated in Figures 1 and 2 of the accompanying drawings. The production line consists of a conveyor 1 for moving bottles 2 at high speed past a print head 6 and ink jet image drier 8 of the ink jet printer, in the indicated direction. While the illustrated embodiment of the invention shows a bottle filling production line, it will be appreciated, by persons skilled in the art, that the drier 8 could be used with any substrate on which ink is printed, such as, cans, cartons, packaging and the like. Typically, the conveyor 1 moves at a speed of 0.51 m/sec to 1.02 m/sec (100 to 200 feet per minute), or more, such that 600 bottles per minute are handled by the production line. As the bottles 2 move into the ink jet printer section they are dewatered (moisture on the bottles may be due to condensation and cleaning, or filling operations) by a dewatering device 4 such as that disclosed in U.S. Patent No. 5,173,988 issued to Bhatia. The dewatering device 4 creates a clean, warm, dry surface on which the ink jet printer is to print an image. Immediately after leaving the dewatering device 4, the bottles pass ink jet printer printhead 6. The print head applies the desired ink image to the bottles, as has been previously described. The bottles with the wet ink jet image printed thereon then immediately pass the drier 8 of the present invention. Referring more particularly to Figures 3 to 5 of the accompanying drawings, the drier 8 consists of an air tight housing 10 defining a hot air chamber 12 therein. Chamber 12 communicates with a plurality of small air nozzles 14 such that air delivered to the chamber 12 under pressure will exit via nozzles 14 at high speed. The nozzles 14 are disposed along the entire length of drier 8 such that the bottles will be contacted by the air for the length of drier 8, as they are moved by conveyor 1. Located within chamber 12 is a heating element 16 (See Figures 3 and 5 of the accompanying drawings). Heating element 16 can consist of a coil, or other controllable heater, capable of heating the air in the chamber 12 to a temperature which is preferrably in a range of between 66°C and 204°C (150 and 400° F), or higher. In the illustrated embodiment, see, in particular, Figure 5 of the accompanying drawings, the air is delivered to chamber 12, under pressure, via air inlet line 18. The location of the air inlet line 18 is such that the air passes through the interior of heating element 16 before entering chamber 12. Other suitable arrangements of the heating element and air inlet can be used provided the air is suitably heated. As illustrated in Figure 5 of the drawings, the air can be supplied to air inlet 18 by a compressor 20, or other suitable air source. Preferably, a regulator 22 is provided to control the pressure and flow rate of the air delivered to inlet 18. The air is delivered to the nozzles 14, under pressure, at a pressure in the range 34.47 kPa to 413.64 kPa (5 to 60 psia). In the preferred embodiment, the air pressure is maintained at a pressure of between 137.8 kPa and 344.7 kPa (20 and 50 psia) and the velocity of the air leaving nozzles 14 is preferably in the range 25.4 m/sec to 50.8 m/sec (5,000 to 10,000 feet per minute). The drier 8 of the present invention is adapted to move a volume of air of approximately 0.0024 m 3 /s (5 cubic feet per minute). The velocity of the air is adjusted by regulating the air pressure in chamber 12 via regulator 22. It is desired to maintain the air velocity as high as possible to maximize drying without physically disturbing the ink drops on the surface of the substrate, i.e. the bottles 2. The specific maximum velocity of the air that can be used depends upon the type of ink, size of the drops and the type of substrate surface. The use of high speed air creates a so-call "skin effect" where a dry layer of ink is quickly formed over the ink drop. This dry "skin" layer facilitates handling of the product by minimizing the smearing, or smudging, of the ink due to contact. The nozzles 14 are angled, as shown by an angle α, in Figure 2 of the accompanying drawings, relative to a line perpendicular to the direction of travel of bottles 2. The value of angle α can be between 0 and 25 degrees. As a result, when the bottles 2 pass the drier 8, in a direction parallel thereto, the air from the nozzles 14 will contact the bottle at angle α. The angling of the nozzles provides a velocity component in the direction of travel of the bottles such that the time, during which the air stream contacts the bottle, is increased. The use of the angled nozzles 14 also directs the air away form the printhead 6 to minimize any adverse effect of the air on the printing process. Moreover, referring to Figure 3 of the accompanying drawings, the drier 8 is mounted such that the nozzles 14 are also at a preferred angle of approximately 25 degrees relative to the horizontal, as shown by an angle B. The drier 8 is angled in order to control the direction the air moves after hitting the bottle 2 and thereby control the width of the area heated by the air such that the entire bottle 2 is not heated. Finally, the nozzles 14 are, in the preferred embodiment, spaced form the passing substrate 2 by approximately 0.48 cm to 0.64 cm (0.19 to 0.25 inches) for maximum results, as shown at 'l' in Figure 3 of the drawings. The speed of drying is affected by three factors: 1) the velocity of air, 2) the time the ink is exposed to the air, and 3) the temperature differential between the ink and the air. As previously described, the air temperature and velocity can be controlled by controlling the heating element 16 and the pressure of the air via regulator 22. The amount of time the ink is exposed to the air is dependent on two factors: 1) the length of drier 8 and 2) the speed at which the bottles 2 are moved by conveyor 1. Because the conveyor speed is determined by the bottle filling operation, or the like, and cannot normally be altered, the time the ink is exposed to the air will depend on the length of the drier 8. The drier 8, in a preferred embodiment, is 28 cm (11 inches) long. The ink can be exposed to the air for a longer period of time by increasing the length of the drier 8, or by using additional driers, arranged in series with the illustrated drier 8. Moreover, the angling of the nozzles 14 also increases the exposure time, as previously described. Thus, the design of the drier of the present invention enables the operator to control the three factors that control drying time quickly and easily to maximize the effectiveness of the system for each application.

Claims: An ink printing system for applying an inked image to a substrate including a dewatering device for removing moisture from the substrate, a printhead for applying the inked image to the substrate, a drier for drying the inked image on the substrate and means for moving the substrate past the dewatering device, the printhead and the drier, characterised in that, the drier (8) comprises an air chamber (12) including a plurality of nozzles (14) in communication therewith, for directing air at the inked image on the substrate (2), and means for delivering air under pressure to said chamber (12), in that the nozzles (14) are adapted to deliver the air at the inked image at high velocity and low volume and in that, said nozzles (14) are angled (α) such that the air has a velocity component in the direction of travel of the substrate (2), effecting an increase in the period of time during which the air contacts the area of the substrate (2) to be dried. An ink printing system, according to claim 1, characterised in that, the nozzles (14) are angled at an angle (α) of between 0 and 25 degrees relative to a line perpendicular to the direction of travel of the substrate (2). An ink printing system, according to claim 1 or 2 characterised in that, the nozzles (14) are at an angle (B) relative to the horizontal to control the direction in which the air moves after contacting the substrate (2) and to thereby control the width of the heated area. An ink printing system, according to claim 3, characterised in that, the nozzles (14) are at an angle (B) of approximately 25 degrees relative to the horizontal. An ink printing system, according to any one of the preceding claims, characterised in that, the velocity of the air directed at the inked image is in the range 25.4 m/sec and 50.8 m/sec (5,000 and 10,000 feet per minute). An ink printing system, according to any one of the preceding claims, characterised in that, the volume of air delivered by the nozzles (14) is in the range 0.00047 m 3 /sec and 0.0047 m 3 /sec (1 and 10 cubic feet per minute). An ink printing system, according to any one of the preceding claims, characterised in that, the air is heated. An ink printing system, according to claim 7, characterised in that, the air is heated to a temperature in the range 37.7°C and 316°C (100 and 600 degrees Fahrenheit). An ink printing system, according to any one of the preceding claims, characterised in that, the air is delivered to the nozzles (14), under a pressure, in the range 37.47 kPa and 413.64 kPa (5 and 60 psia). An ink printing system, according to any one of the preceding claims, characterised in that, a heating element (16) is located in the chamber (12). An ink printing system, according to any one of claims 1 to 8, characterised in that, a heating element is located outside the chamber (12). An ink printing system, according to any one of the preceding claims, characterised in that, the system further includes means (22) for regulating the pressure of the air delivered to the chamber (12) thereby to control the speed of air from the nozzles (14). An ink printing system, according to any one of the preceding claims, characterised in that, the air creates a skin effect on the ink such that the outer surface of the drops is dried first. An ink printing system, according to any one of the preceding claims, characterised in that, the nozzles (14) are angled away from the ink jet printer head (6).

Inventors: BHATIA CHANDRAKANT R, KUHLIN STEVEN S, BHATIA, CHANDRAKANT R., KUHLIN, STEVEN S.
Applicants: VIDEOJET SYSTEMS INT, VIDEOJET SYSTEMS INTERNATIONAL, INC.
Application year: 1994
Main classification: B41J2
IPC codes: B41J3, F26B15, F26B21, B41J11, B41J2